1. Field of the Invention
The present invention relates to the art of adjusting valve clearances in an overhead cam internal combustion engine, and more particularly to the method and apparatus for back biasing the valve spring.
2. Background of the Invention
In internal combustion engines, air is taken into, and forced out of the combustion chambers through carefully timed operation of valves opened and closed in a combustion cycle or Otto cycle, in most designs by cam lobes mounted on, or integral with, camshafts. The valves seat within the air intake or exhaust ports, and are opened on the engagement of a cam lobe with the valve assembly, by engaging a cam follower which is connected with a valve spring through a valve spring retainer. The cam lobe engages the cam follower either directly, as through a shim, or indirectly, which is usually through a rocker arm assembly. The valve spring biases the valve into the closed position, in which position the valve head is seated within the port. Because of the great number of repetitive valve operations during the cycles of the camshaft during operation, the valve head wears on the valve seat structure and itself, so that the valve head will, with time, sit deeper within the valve seat in the cylinder head.
When the valve seating structure deteriorates, it is likely that the. valve will seat too far within the seating structure, reducing the clearance between the cam and the cam follower. Correction of the clearance can be accomplished by replacing the cam follower shim or other clearance adjusting instrument. Moreover, the clearance between the cam and the cam follower is sometimes important in fine tuning an engine for special performance.
The pressure on the cam follower-to-cam lobe interface passes through the shim or similar device. When it is desired to adjust the cam-to-cam follower clearance, either for maintenance or for performance reasons, the adjustment therefore is normally made by replacing the shim or similar device. To make such a replacement, it is necessary to obtain relief from the valve spring pressure.
Furthermore, the shim is very small, and normally is placed in a very inaccessible location. The shim, for example, is on the order of 0.150 inches thick. The pressure on the shim is on the order of, e.g. 160 to 220 pounds per square inch (xe2x80x9cpsixe2x80x9d) the pressures are on the order of as much as 600 psi.
Various methods and tools have been designed to assist the automobile mechanic in relieving the valve spring pressure. For example, Kammeraad, U.S. Pat. No. 3,979,811 teaches an overhead camshaft and valve tool that can be attached to the cylinder head, the ultimate objective of which is to relieve the pressure of the cams on the cam followers. The tool must be attached first to the cylinder head below the cam shaft, with shoes that each has a flange that must be positioned laterally of the cam followers. The flanges must be inserted between the cam shaft and the cam followers so that the flange in each case will be engaged by a corresponding cam lobe to depress the corresponding cam follower and valve spring. A bolt for each cam follower is positioned in a space adjacent to the cam follower but not in-line or over the cam follower, and is selectively connected to the flange through the shoe, which is rotated about a fulcrum in the form of a rod. When the cam lobe for each cam engages its corresponding cam follower through the flange, the bolt is then screw-turned into a position to maintain its corresponding cam follower in the depressed position against the valve spring""s bias. Each cam follower is made to be depressed in like manner. The camshaft, with all of the valve springs"" pressure thus relieved, can then be removed.
Other tools for relieving the pressure on the cam follower from the valve springs, are shown and described in, for examples, Mote, et al., U.S. Pat. No. 3,977,064, Johnson, U.S. Pat. No. 4,446,608 and Zdral, U.S. Pat. No. 5,499,434. Mote. et al. teaches a series of steps for the removal and replacement of a valve spring assembly in a push rod and rocker arm motor. The push rod must be removed and the rocker arm must be disengaged, after which a plate is inserted over a pair of valve springs, and a threaded shaft is used to move the plate and consequently the pair of springs against their bias.
In each of the Johnson and the Zdral teachings, an elongated lever is rotated about a line of rotation to depress the valve spring. In Johnson, the lever is hooked onto a pivot shaft and a leg attached to the other end of the lever engages the retainer for the spring which is depressed. In Zdral, the lever is hooked around the camshaft itself, making the camshaft itself act as the pivot line. Another location on the lever engages a depressor member which depresses a retainer connected to the valve spring. Upon rotating the lever about the pivot line, the depressor member depresses the spring""s retainer. In both of these devices, as well as in the device of Kammeraad, identified above, the lever must be locked in the spring-depressed mode to prevent the spring from applying pressure back against the cam or cam lobe. It has been known for the locking mechanism to surprise the mechanic and become unlocked. The result can be injury as well as sore knuckles.
In many engine designs, furthermore, there is no space or room for an elongated lever to be inserted into the cavity around the shim""s location.
It is still desired, therefore, to provide a valve spring pressure relief apparatus that can be mounted so as to contact the valve spring cam follower directly, without the necessity of removing any part in the linkage between the cam lobe and the cam follower before the replacement of any part. It is desired, further, to provide a valve spring pressure relief apparatus that has a direct, or straight line of pressure without the necessity of having pressure transferring apparatus that is articulated around the camshaft. It is desired, furthermore, to provide a valve spring pressure relief apparatus that does not rely upon the working of a lever about a fulcrum or pivot line. Yet further, it is desired to provide a valve spring pressure relief apparatus which, when depressing the valve spring, does not require a locking mechanism to remain and be maintained in the spring-depressed state.
In brief, in accordance with one aspect of the present invention, a valve clearance adjusting tool has a body which is mountable onto a cam bearing cap of an overhead cam internal combustion motor. A threaded screw is selectively moveable in a linear direction through the body of the valve clearance adjusting tool, to linearly position a dowel pin and its foot positioned linearly to the threaded screw. The valve clearance adjusting tool is removably mounted to a cylinder head through a cam bearing cap by an already existing cam bearing cap bolt. The methods of the present invention include the engagement by the dowel pin foot directly onto a corresponding cam follower on its edge without engaging the clearance adjustment shim, by way of movement of the threaded screw to depress the valve spring against the spring""s bias, thereby enlarging the space between the cam follower and the cam and allowing better ease of access to the shim positioned on the head of the cam follower.
Other novel features which are .believed to be characteristic of the invention, both as to organization and methods of operation, together. with further objects and advantages thereof, will be better understood from the following description in which preferred embodiments of the invention are described by way of example.